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CCFS-Macquarie University, University of WA, Geological Survey WA

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1 CCFS-Macquarie University, University of WA, Geological Survey WA
 Lithosphere in craton margins and adjacent orogens: seismic structure and tectonic implications Huaiyu Yuan CCFS-Macquarie University, University of WA, Geological Survey WA Australia IGG-CAS Jan 1

2 Building craton lithosphere
Lee et al., Annu. Rev. Earth Planet. Sci, 2011

3 Destroying craton lithosphere
Lee et al., Annu. Rev. Earth Planet. Sci, 2011

4 High resolution image along craton margins/orogens
investigate deep crustal architecture to better target mineral deposit systems: how crustal structure focuses magmas and fluids; potential fluid pathways;

5 High resolution image along craton margins/orogens
Temporary line/2D array setup; 1-2 year deployments Array processing methods: body wave tomography; receiver functions; ambient noise Few 100s km lateral structure with 10s km lateral resolution: better than TA resolution Observations regarding craton stabilization and reworking investigate deep crustal architecture to better target mineral deposit systems: how crustal structure focuses magmas and fluids; potential fluid pathways;

6 High resolution image along craton margins/orogens
Temporary line/2D array setup; 1-2 year deployments Array processing methods: body wave tomography; receiver functions; ambient noise Few 100s km lateral structure with 10s km lateral resolution: better than TA resolution Observations regarding craton stabilization and reworking Examples in Wyoming craton and surrounding orogens/margins Building a craton: subduction polarity reversal; Wedge tectonics Destroying mechanism: plume erosion; mid-crustal sill; lower crustal flow; magmatic underplating (7.x layer). investigate deep crustal architecture to better target mineral deposit systems: how crustal structure focuses magmas and fluids; potential fluid pathways;

7 Wyoming craton Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007

8 Wyoming craton Proterozoic orogens along 3 sides
Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007 Proterozoic orogens along 3 sides Cheyenne belt extensively studied West margin unclear; affected by Yellowstone hotspot system Foster et al., 2006

9 Wyoming craton Yuan et al. 2011; Modified from Whitmeyer and Karlstrom 2007 Upper mantle dipping reflectors from active imaging along north border: imbricated slab Gorman et al., 2002 Foster et al., 2006

10 Geophysical lines/arrays
Yuan and Dueker 2010; Modified from Mueller and Frost 2006

11 Southern margin: The Cheyenne slab
Archean/Proterozoic ( Ga; Karlstrom 1988) southward subduction; lack of subduction related rocks on the Archean side; dip of mylonite zones along the shear zone on the surface

12 Southern margin: The Cheyenne slab
CD-ROM lines image the structure using P- and S-wave body wave tomography (Yuan and Dueker 2005)

13 Southern margin: The Cheyenne slab
North dipping high velocity found beneath the Cheyenne belt P-wave S-wave Model Error Spike test

14 Southern margin: The Cheyenne slab
North dipping high velocity found beneath the Cheyenne belt Proposed as a fossil slab segment, the Cheyenne slab Consistent with north-dipping anisotropy modelled by shear wave splitting Requires anisotropy present in the “slab” P-wave S-wave Model Error Spike test

15 Southern margin: The Cheyenne slab
Subduction polarity reversal is proposed

16 Southern margin: The Cheyenne slab
High velocity Cheyenne slab observed along the whole southern margin Receiver function CCP structure follows the slab interface Yuan and Dueker, 2010

17 Southern margin: Imbricated Moho
Receiver function CCP image across the Cheyenne belt Laramie array: 30 sites with 2-km spacing; 1 year operation No Moho in active reflection images

18 Southern margin: Imbricated Moho
Imbricated Moho: Archean + Proterozoic Moho Consistent with northward subduction P-wave CCP Stacking Archean Moho Proterozoic Moho

19 Southern margin: Imbricated Moho
Imbricated Moho: Archean + Proterozoic Moho Consistent with northward subduction S-wave CCP Stacking P-wave CCP Stacking Archean Moho Proterozoic Moho Hansen and Dueker 2009

20 Southern margin: The Wedge tectonics
The Wedge tectonics: stronger Archean lithosphere vs weaker (more deformable) juvenile terrane lithosphere Archean Moho Proterozoic Moho Snyder 2002

21 Note red is positive gradient in 2 and 3!
Southern margin: The Wedge tectonics The Wedge tectonics along the Cheyenne belt Note red is positive gradient in 2 and 3! Yuan and Dueker, 2010

22 Western margin: Yellowstone plume
Plume interacting with the Archean lithosphere Ambien noise image of the crust and shallow upper mantle USGS website

23 Western margin: Yellowstone plume
Plume interacting with the Archean lithosphere Ambien noise image of the crust and shallow upper mantle Stachnik et al. 2008

24 Western margin: Yellowstone plume
Thinning of lithosphere under the hotspot track Stachnik et al. 2008

25 Stachnik et al. 2008; Yuan et al. 2005
Western margin: Yellowstone plume Consistent with body-wave Yellowstone plume image Stachnik et al. 2008; Yuan et al. 2005

26 Mid-crustal sill (MCS)
Western margin: Yellowstone plume Magma injection into the crust: mid-crustal sill and lower crustal flow Mid-crustal sill (MCS) Stachnik et al. 2008

27 Western margin: Yellowstone plume
Magma injection into the crust: mid-crustal sill and lower crustal flow Peng and Humphreys, 1998

28 Western margin: Yellowstone plume
Magma injection into the crust: mid-crustal sill and lower crustal flow Stachnik et al. 2008

29 Western margin: Yellowstone plume
Earlier magma injection in the Archean crust: 7.x layer 7.x P-wave velocity from active source modeling Stachnik et al. 2008 7.x layer

30 Western margin: Yellowstone plume
7.x layer in receiver functions, active source imaging and gravity modeling Yuan et al. 2010 Snelson et al. 1998

31 Summary Paleo-subduction and imbrication played an important role in craton stabilization by docking Proterozoic terranes to the Archean craton Inconsistent observations with surface geology suggest subduction polarity reversal Yellowstone plume strongly modified Archean craton by eroding (thinning) the lithosphere; Also increased crust volume by injecting magma into the crust

32

33 Magma injection & forming of Mid-crustal sill

34 Mid-crustal sill induces lower crustal flow

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